This invention relates to catalysts for olefin polymerization, and more particularly to supported metallocene catalysts wherein a reaction product of a metallocene compound and aluminoxane is supported on a fine particulate inorganic support, and processes for the production thereof. The invention also relates to processes for the production of olefin polymers by polymerizing olefin(s) in the presence of a catalyst system comprising the supported metallocene catalyst in combination with an organoaluminum compound.
Olefin polymers such as polypropylene and polyethylene have been extensively used in the field of various moldings such as films, fibers and injection-molded articles, because of their good mechanical properties, good chemical resistance and very useful balance with economy. As the catalyst for olefin polymerization for the manufacture of olefin polymers, the prior art has used a catalyst comprising an inorganic transition metal catalyst component such as titanium trichloride, titanium tetrachloride or the mixture thereof supported on a support such as magnesium chloride, in combination with an organoaluminum compound, what is called Ziegler-Natta catalyst system.
In recent years, metallocene catalyst systems comprising an organic complex of a transition metal, what is called a metallocene compound in combination with aluminoxane have been proposed as the catalysts for olefin polymerization, instead of prior Ziegler-Natta catalyst system. Olefin polymerization using these metallocene catalyst systems produces olefin polymers having narrow molecular weight distribution width (Mw/Mn), and also olefin copolymerization using them produces more homogeneous olefin copolymers wherein comonomers are copolymerized homogeneously, than those using prior Ziegler-Natta catalyst system.
These known metallocene catalyst systems include homogeneously mixed metallocene catalyst systems comprising a metallocene compound and aluminoxane and supported metallocene catalyst systems having a metallocene compound and/or aluminoxane supported on a finely particulate support.
Homogeneously mixed metallocene catalyst systems are applicable to a solution polymerization process, in view of industrial production of olefin polymers. When these catalyst systems are applied to a gas phase polymerization process and a slurry polymerization process generally employed in the Ziegler-Natta catalyst system, bulk density of the resulting olefin polymers is extremely low and the particle morphology is also poor. Further, the amount of aluminoxane used together with the metallocene compound in the homogeneous metallocene catalyst system is more than that of general organoaluminum compound used in prior Ziegler-Natta catalyst system, and also aluminoxane is more expensive than general organoaluminum compound. Therefore, there is a problem in the application of the homogeneously mixed metallocene catalyst system to industrial production of olefin polymers.
The supported metallocene catalyst systems have been proposed as the catalysts for olefin polymerization which can be employed in the gas phase and slurry polymerization processes. In these catalyst systems, the amount of aluminoxane used may be restricted, and bulk density and particle morphology of the resulting olefin polymer may be improved.
For instance, JPA 5-155931, JPA 8-104691, JPA 8-157515 and JPA 8-231621 disclose supported metallocene catalysts, preactivated supported metallocene catalysts, processes for the production thereof, and processes for the production of olefin polymers by polymerizing olefins using these catalysts. The working examples for preparing the supported metallocene catalyst described therein include (i) the example wherein silica and aluminoxane are contacted in toluene, and with or without washing with toluene, a toluene solution of the metallocene compound is added and contacted, and then the product is separated and washed with hexane to have aluminoxane and metallocene compound supported on silica, and (ii) the example wherein a mixed solution of aluminoxane and metallocene compound in toluene is added to a silica/toluene slurry, the product is separated by decantation and washed three times with hexane to have aluminoxane and metallocene compound supported on silica. In these examples, the temperature is controlled in each contact with silica, aluminoxane and metallocene compound by elevating or lowering it between 0xc2x0 C. and 95xc2x0 C. in multistage and finally lowering it to 60xc2x0 C., and then a washing step with hexane is performed. Since there is no specific reference to the temperature in the washing step, it is presumed to be between 60xc2x0 C. and ambient temperature.
WO 94/28034 (JPA 8-511044) discloses a supported metallocene catalyst which is prepared by contacting a metallocene compound represented by a specific chemical formula with aluminoxane in the presence of a solvent, contacting the resulting soluble reaction product with a porous support such as silica, removing the solvent and drying the supported catalyst; the supported metallocene catalyst which is preactivated by prepolymerizing the supported metallocene catalyst with one or more olefinic monomer(s); and a process for the preparation thereof as well as a process for the production of an isotactic polypropylene using this catalyst system. The process for the preparation of the supported metallocene catalyst comprises the step of contacting a reaction product of a soluble metallocene compound and aluminoxane with a porous support in a solvent, heating the supported product to about 70xc2x0 C. under reduced pressure and evaporating the solvent until the product becomes a xe2x80x9cmudxe2x80x9d stage and all the solvent is removed, thereby preparing the supported metallocene catalyst, and the step of preactivating the supported metallocene catalyst by suspending again said catalyst in a hydrocarbon and prepolymerizing the catalyst with olefin(s).
The above-mentioned known art of the supported metallocene catalyst has accomplished some improvement in an olefin polymerization activity of the metallocene catalyst, reduction in the amount of aluminoxane used and improvement in bulk density and particle morphology of polyolefin obtained by using the metallocene catalyst.
On the other hand, there are many problems that reduction in stereoregularity of isotactic polypropylene should be controlled, that an olefin polymerization activity should be improved and that a process step for the preparation of the supported metallocene catalyst should be rationalized.
An object of the invention is to provide a supported metallocene catalyst for olefin polymerization having a high olefin polymerization activity.
Another object of the invention is to provide an improved process for the preparation of the supported metallocene catalyst.
Further object of the invention is to provide a process for the production of an olefin polymer using the supported metallocene catalyst.
In the present invention, polymerization of olefin(s) using the above supported metallocene catalyst can achieve the reduction in amount of aluminoxane used, control of the reduction in stereoregularity of the resulting olefin polymer and improvement in bulk density and particle morphology of the resulting olefin polymer.
The present inventors have made earnest studies in an effort to accomplish the above mentioned objects and, as a result, have found that a specific supported metallocene catalyst has dramatically improved olefin polymerization activity, the supported catalyst being prepared by reacting a metallocene compound with aluminoxane in an aromatic hydrocarbon solvent, supporting the reaction product on a fine particulate inorganic support at a relatively high temperature, and washing the resulting solid product with an aliphatic hydrocarbon at a relatively low temperature, thus leading to completion of the invention.
The present invention provides a supported metallocene catalyst for olefin polymerization comprising solid fine particles which comprise a reaction product of a metallocene compound and aluminoxane supported on the finely particulate inorganic support, said solid fine particles being produced by carrying out in order the following steps of:
(a) reacting a metallocene compound with an aluminoxane in an aromatic hydrocarbon solvent to form a reaction product,
(b) contacting the reaction product with a finely particulate inorganic support at a temperature of 85 to 150xc2x0 C. in the presence of any aromatic hydrocarbon solvent to form a solid product having the reaction product supported on said inorganic support, and
(c) washing the solid product with an aliphatic hydrocarbon solvent at a temperature of xe2x88x9250xc2x0 C. to +30xc2x0 C.; and also a process for the preparation of the supported metallocene catalyst.
The supported metallocene catalyst of the present invention includes that which is preactivated by further carrying out, subsequently to step (c), step (d) of prepolymerizing an olefin by introducing the olefin into a slurry of the solid fine particles dispersed in any aliphatic hydrocarbon solvent.
Another aspect of the present invention is a process for the production of an olefin polymer which comprises polymerizing olefin(s) in the presence of a catalyst system of the above-mentioned preactivated or non-preactivated supported metallocene catalyst in combination with an organoaluminum compound.